#include "apue.h"
#include <fcntl.h>
#include <sys/mman.h>

#define COPYINCR (1024*1024*1024)

int 
main(int argc, char *argv[]) {
	int fdin, fdout;
	void *src, *dst;
	size_t copysz;
	struct stat sbuf;
	off_t fsz = 0;

	if (argc != 3) {
		err_quit("usage: a.out fromfile tofile");
	}

	if ((fdin = open(argv[1], O_RDONLY)) < 0) {
		err_sys("can't open %s for reading", argv[1]);
	}

	if ((fdout = open(argv[2], O_RDWR | O_CREAT | O_TRUNC, FILE_MODE)) < 0) {
		err_sys("can't open %s for writing", argv[2]);
	}

	if (fstat(fdin , &sbuf) < 0) {
		err_sys("fstat error");
	}

	if (ftruncate(fdout, sbuf.st_size) < 0) {
		err_sys("ftruncate error");
	}

	while (fsz < sbuf.st_size) {
		if ((sbuf.st_size - fsz) > COPYINCR) {
			copysz = COPYINCR;
		} else {
			copysz = sbuf.st_size - fsz;
		}

		if ((src = mmap(0, copysz, PROT_READ, MAP_SHARED, fdin, fsz)) == MAP_FAILED) {
			err_sys("mmap error for input");	
		}
		if ((dst = mmap(0, copysz, PROT_READ | PROT_WRITE, 
						MAP_SHARED, fdout, fsz)) == MAP_FAILED) {
			err_sys("mmap error for output");	
		}

		memcpy(dst, src, copysz);
		munmap(src, copysz);
		munmap(dst, copysz);
		fsz += copysz;
	}

	exit(0);
}
